1. Field of the Invention
This invention relates to a short circuit phase identification method for a motor control device of an electric automobile or a hybrid vehicle, and more particularly to a short circuit phase identification method for identifying a short circuit phase of a motor control device from an electric current generated by the rotation of a motor.
2. Description of the Related Art
A demand has recently grown for environmentally friendly electric automobiles and hybrid vehicles. In a hybrid vehicle, part of the engine power is transmitted to a drive shaft via a power distribution mechanism provided with a first motor generator. The remaining power is recovered as electric power by the first motor generator, and the recovered electric power may be used to charge a secondary battery or to drive a second motor generator.
In a motor control device of an electric automobile or a hybrid vehicle, an alternating current motor is used and feedback control of a drive current is performed for each phase. In the motor control device, a current offset is adequately detected from a detected signal of a current sensor, measuring accuracy of the current sensor may be enhanced by using a configuration in which the current is learned over time, and adequate feedback control, state monitoring of the motor generator, and malfunction detection are implemented.
In the above-described hybrid vehicle, for example, when a one-phase short circuit occurs in the first motor generator, a brake torque is applied to the engine by a torque in the reverse rotation direction and undesirable torque fluctuations sometimes occur. Accordingly, Japanese Patent Application Publication No. 2007-28733 (JP-A-2007-28733) discloses a feature that resolves a problem causing the brake torque when a short circuit malfunction occurs in the first motor generator.
Furthermore, Japanese Patent Application Publication No. 2006-246564 (JP-A-2006-246564) describes a feature relating to a malfunction diagnostic device that accurately detects a plurality of malfunction modes, more particularly to a malfunction diagnostic device that can distinguish between a malfunction occurring in a boost converter from that in an inverter circuit by using an offset-corrected current sensor.
JP-A-2007-28733 indicates that a three-phase short circuit control is executed, by which when one phase or two phases of a motor generator are short circuited, the remaining phase is also short circuited to obtain a three-phase short circuit state and the short circuit malfunction control means is provided to control the engine speed so that the rotational speed of the motor generator does not fall within a predetermined range after a short circuit malfunction occurs.
When a short circuit malfunction occurs in transistors provided above and below each phase arm of the inverter when one or two phases of the motor generator are short circuited, electric current flows even in a non-energized state. Consequently, the offset value of the current sensor is changed by zero point adjustment. The resultant problem is that fluctuations of the offset point when a malfunction has occurred adversely affects subsequent feedback control, state monitoring, and malfunction diagnostics.